This invention relates generally to ink jet apparatus, and more particularly to ink supplies for an ink jet apparatus.
Ink jet printers, particularly those of the impulse or the drop-on-demand types, have special ink supply requirements since the usual method replacing ink expelled from the jets is by capillary action. Prior art printers include ink supply systems which typically comprise a single reservoir containing ink, a manifold for supplying ink to an array of jets, and some form of flow path from the manifold to the reservoir. In apparatus having a large number of jets within the array, for example a 32-channel array, there is a problem of minimizing cross talk in the form of pressure disturbances and waves through the manifold.
A cross talk type of disturbance is generally characterized by the development of a pressure impulse in the manifold due to the small volume liquid injection derived from the pulsing of a jet. In order to reduce such cross talk, one standard arrangement has been to design a manifold to present inlet restrictor paths with as large a fluidic compliance as possible, the magnitude of the pressure wave being inversely proportional to such compliance. The value of compliance is a function of both the compressability of the liquid volume and flexibility of the wall surrounding the liquid. Such manifold compliance is also important to minimize the effects of external shock and vibration which, in certain situations, can lead to depriming of the apparatus. As a result, many arrangements have been proposed wherein a large compliance is achieved by forming a major portion of the manifold wall with a thin compliant diaphragm.
The construction of a manifold so as to maximize its compliance generally requires an expansion of the size of the manifold in order to achieve the necessary flexural compliance of the diaphragm. This results in an ink jet head which is larger than optimum, requiring the ink reservoir to be situated at a substantial distance. Such a requirement has lead to a variety of designs which generally contain a tortuous flow path from the reservoir to the manifold. In those cases, even though the reservoir itself represents a nearly infinite fluidic compliance, the impedence of the connecting path does not allow the manifold to take advantage of such compliance. Thus, the manifold design itself must essentially take on the entire job of minimizing the cross talk and the effects of external shock or disturbance, and generally fails to take advantage of the beneficial compliance characteristics of the reservoir. Arrangements for optimizing the compliance characteristics of the manifold have, therefore, resulted in a tradeoff of a larger manifold configuration for a larger print head and relative displacement of the reservoir away from the array of ink jets. Accordingly, the problem of cross talk is solved at the expense of requiring a larger and bulkier print head which is clearly disadvantageous.
Another problem which results from a large sized manifold is that of air bubble generation at the time of filling the apparatus with ink. The feeding of ink from a relatively small inlet to a relatively large manifold may result in excessive air bubble generation. Of course, if the manifold is large, then a further space penalty must be paid if the inlet tube is made large so as to reduce the air bubble problem.
One suitable prior art approach is disclosed in copending U.S. patent Application Ser. No. 661,794, filed Oct. 16, 1984, assigned to the assignee of the present invention, and incorporated herein by reference. In that approach, the ink jet apparatus provides a reservoir having at least a portion located in very close proximity to the ink jet chamber portion which contains an array of ink jet chambers, and a manifold system for feeding ink from the reservoir to the chambers including a narrow manifold with a very short feed tube connecting the manifold to the reservoir, the feed tube and the manifold having substantially matching cross-sectional forms. The narrow manifold is suitably constructed as a groove in a transducer support structure, such that the manifold does not contain any high compliance element. As a result, the short length of the inlet feed tube and the matching of such a short tube with the manifold ensures that the high compliance characteristic of the reservoir is effectively presented to the chamber inlets, thereby reducing cross talk and reducing the trapping of air when the apparatus is filled with ink.
While the apparatus disclosed in the aforedescribed copending U.S. patent Application Ser. No. 661,794, now abandoned is generally suitable for use with inks such as hot melt or phase change inks, the use of hot melt or phase change inks nevertheless creates additional design requirements with respect to the reservoir system. As is well known, a hot melt or phase change ink of the type utilized in an ink jet is characteristically solid at room temperature. When heated, the ink will melt to a consistency so as to be jettable. For a discussion of the characteristics of such ink and the use thereof in ink jet apparatus, references to U.S. Pat. No. 4,390,369 and pending U.S. Application Ser. No. 644,542, filed Aug. 27, 1984; Ser. No. 909,007, filed Sept. 16, 1986; and Ser. No. 938,334, filed Dec. 3, 1986 all assigned to the same assignee as this invention and incorporated herein by reference.